1. Field of the Disclosure
This invention is related to image sensors. In particular, embodiments of the present invention are related to three dimensional image sensors.
2. Background
Interest in three dimensional (3D) cameras is increasing as the popularity 3D applications continues to grow in applications such as imaging, movies, games, computers, user interfaces, and the like. A typical passive way to create 3D images is to use multiple cameras to capture stereo or multiple images. Using the stereo images, objects in the images can be triangulated to create the 3D image. One disadvantage with this triangulation technique is that it is difficult to create 3D images using small devices because there must be a minimum separation distance between each camera in order to create the three dimensional images. In addition, this technique is complex and therefore requires significant computer processing power in order to create the 3D images in real time.
For applications that require the acquisition of 3D images in real time, active depth imaging systems based on the optical time of flight measurement are sometimes utilized. Time of flight systems typically employ a light source that directs light at an object, a sensor that detects the light that is reflected from the object, and a processing unit that calculates the distance to the object based on the round trip time that it takes for light to travel to and from an object. In typical time of flight sensors, photodiodes are often used because of the high transfer efficiency from the photo detection regions to the sensing nodes.
A continuing challenge with the acquisition of 3D images is that the required processing must occur very quickly in order for the 3D image acquisition system to resolve time differences. With such short response times required for real time applications, the overall transient currents in 3D image sensors can be very high because all of the pixels in the 3D sensors can detect light at substantially the same time. The very high transient currents can occur in a very short amount of time and consequently cause noise and voltage drops on the power line, which will have detrimental effects on the working states of all of the pixels on the 3D sensors.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.